2. Outcrops
Where rocks meet the surface
Shape of outcrop depends on the shape of the
surface and shape of structure
3. Conours
‡ a curve along which the function has a
constant value
‡ Topographic/ elevation Contours: Lines of
equal elevation
‡ Never crosses each other
8. Outcrop Patterns ± Cont¶d
‡ Vertical Beds: have
straight outcrop that
ignore the contours
9. Outcrop Patterns ± Cont¶d
‡ Dipping Beds: have curved outcrop that cut across the
contours
10. Outcrop Patterns ± Cont¶d
‡ Dip Direction: is recognized by the V in Valley Rule: an
outcrop of a dipping rock bends round a V shape where it
crosses a valley, and the V of the outcrop points (like an
arrowhead) in the direction of dip, regardless of the direction
of valley slope and drainage
‡ The rule does not apply in areas of low dip, where outcrops
nearly follow contours, so point upstream. On level ground,
dipping beds have straight outcrops along the direction of
strike
11. Outcrop Patterns ± Cont¶d
‡ Succession is recognized by younger rocks
coming to outcrop in direction of dip.
‡ Conversely, if succession is known, the dip is
in the direction of younger outcrops ± the
easiest way to recognize dip on most maps
12. Outcrop Patterns ± Cont¶d
‡ Width of outcrop is greater at lower dips ± and
on thicker beds
13. Recognition of Structures
‡ Unconformity is recognized where one
outcrop (of a younger bed) cuts across the ends
of outcrops of older beds
14. Recognition of Structures
‡ Faults are usually marked and keyed on maps.
They may cut out, offset or repeat outcrops of
beds. Fault dip is recognized by V in Valley
Rule. is recognized where one outcrop (of a
younger bed) cuts across the ends of outcrops
of older beds
15.
16. Recognition of Structures
‡ Folds are recognized by changes in dip
direction, and also by outliers and inliers not
due to topography.
‡ Most important, folds are recognized by bends
in outcrop: any outcrop bend must be due to
either a fold or a topographic ridge or valley.
17. Drawing a Cross-Section
‡ A cross-section is drawn by projecting the data
from a single line on the map onto a profile of
the same scale
‡ The topography and each geological boundary
are constructed individually from the relevant
contours, whose intersections on the section
line are projected to their correct altitudes on
the profile
